An internal combustion engine of an automotive vehicle etc. has a knock sensor capable of detecting a knocking phenomenon and performs control to prevent the occurrence of a knocking phenomenon based on a detection signal outputted from the knock sensor and, more specifically, ignition retard control to the ignition timing of a spark plug based on the output signal of the knock sensor.
As such a knock sensor, there is known a so-called center-hole type non-resonant knock sensor having in the center thereof a mounting hole for mounting the knock sensor on a cylinder block etc. of the internal combustion engine (see Patent Document 1). This type of knock sensor includes a metal shell, an insulator, a piezoelectric element and a weight. The metal shell has a cylindrical portion and a flange portion formed at one end of the cylindrical portion. The insulator, the piezoelectric element and the weight are each annular in shape and are fitted around an outer circumference of the cylindrical portion in order of mention from the flange portion side. The piezoelectric element is fixed between the flange portion and the weight by screwing the weight to a male thread on the outer circumference of the cylindrical portion. The inner unit (sensor body) of the knock sensor, in which the insulator, the piezoelectric element and the weight are fixed in the metal shell, is covered with a resin. The mounting hole is herein defined by an inner surface of the cylindrical portion.
In the above knock sensor, a plurality of cuts are formed axially in a female thread of the weight as an introduction passage of the resin to establish insulation between an outer circumferential surface of the cylindrical portion and an inner circumferential surface of the piezoelectric element. This eliminates the need to provide a separate resin injection hole or groove and enables a reduction of manufacturing cost.